Editor's note: Tim Lister produced "Cruise to Disaster," a CNN documentary on the capsizing of the Costa Concordia.
(CNN) -- The last few years have seen a rash of engine fires aboard cruise ships -- many of which have led to an almost total loss of electrical power. Passengers on board the Carnival Triumph are but the latest to endure the consequences: a lack of hot food and water, a loss of air conditioning and refrigeration, sanitation systems on the verge of collapse.
Beyond these inconveniences are more serious issues: a loss of engine-power to the vessel and the lack of stabilization. If a ship is on the high seas in rough weather there is a greater risk of injury as the vessel pitches and rolls. The situation is further aggravated if tugs are days -- not hours -- away.
The U.S. National Transportation Safety Board warned after one such fire that "Hazardous situations that may result from a ship losing propulsive power include vessel grounding, inability to avoid severe weather conditions, and passenger evacuation at sea."
No backup power
Many wonder why such huge ships have inadequate backup power in the event of an electrical failure.
Modern cruise liners are like floating towns, 10 or 15 floors high. They carry 3,000 to 4,000 passengers and draw an immense amount of electrical power. If the main power supply fails, auxiliary systems can supply only a fraction of what's needed.
Jay Herring, a former senior officer with Carnival Cruise Lines who served on the Triumph, said: "The Triumph is normally powered by six diesel-electric generators. Each one is the size of a bus, and 80% of the electricity used on board goes towards propulsion."
"So if you take those away even if you have a backup generator, you're only going to be able to provide lighting in limited areas and you're certainly not going to be providing ventilation for a vessel that is the size of three football fields."
The 1,000 toilets on board, for example, require a massive amount of electricity to work the suction system.
As for the generator airlifted to the Triumph on Tuesday by the U.S. Coast Guard, Herring said: "It would only be like a Band-Aid on a gashing wound. It might provide a little bit of relief but there's no way that we're going to be able to drop a backup generator for propulsion."
Catalog of engine fires
There has been a spate of engine fires aboard passenger ships around the world in recent years.
2011: In the Indian Ocean, the Costa Allegra suffered an engine fire that left it without power for three days in tropical heat of nearly 100 degrees Fahrenheit. The fire broke out in the electrical generator room. There were no casualties but tugs were needed to tow the ship to Mahe in the Seychelles. As with the Triumph, backed-up toilets and a lack of water were among the problems. Passengers said after disembarking they were fearful of pirates or rough weather in the stranded ship.
2011: The Azamara Quest -- in the midst of a Southeast Asian cruise -- was disabled by an engine fire and drifted in southern Philippine waters. Propulsion was restored the next day and the vessel limped into Sandakan in Malaysia.
2011: The Ocean Star Pacific, a Mexican liner with 522 passengers and 226 crew, was stranded by a generator fire a few miles off the Pacific coast of Mexico. The passengers were evacuated.
2011: On September 15 a fire in the engine room of the MS Nordlys killed two of the crew. All 207 passengers were taken off the ship, which was off the coast of Norway.
2010: During the early hours of November 8 an engine room fire on the Carnival Splendor 200 miles off the coast of Mexico disabled the ship. The fire broke out in the aft engine room and took several hours to extinguish. No one was hurt but the cruise director, John Heald, said later that "the smoke was so intense and so thick that, even with breathing apparatus on, the teams could not get close to the source" of the fire.
Carnival CEO Gerry Cahill said later there had been a "catastrophic failure of diesel generator No. 5." But at the time he said he doubted any of the other ships in the company's fleet were at risk.
2009: A fire started in the engine room of The Royal Princess while on a cruise in the Mediterranean, with 1,126 people on board. The fire broke out soon after the ship left Port Said. Partial engine power was restored the next morning.
These incidents were caused by different problems. In the case of the Splendor, the heat generated by the fire damaged two engine control switchboards directly above and melted electrical cabling, causing a total loss of electrical power on board and the failure of the forward engine room.
The U.S. Coast Guard said the ship's CO2 firefighting system had failed to operate correctly due to leaks, poor maintenance and component failures.
The repairs involved replacing more than 100 miles of electrical cable, according to Carnival. Among other improvements introduced or recommended: better insulation of cables and switchboards, and more fire suppression systems.
After two fires on board cruise ships in the 1990s, the then-chairman of the National Transportation Safety Board said the cruise industry needed to do more in the way of training and fire prevention. The NTSB found that a fire on board the Liberian-registered Ecstasy, operated by Carnival, had been caused by a fire in the laundry room sparked by unauthorized welding.
A fast-expanding industry
The cruise line industry has expanded fast as vacations at sea have come within the budgets of more people and the different operators have competed for customers. By the end of 2010, there were an estimated 215,000 cabins in the industry worldwide. Carnival and its subsidiaries account for nearly half that capacity.
Taking a cruise remains a very safe vacation. According to the Cruise Line Industry Association, known as CLIA, there were 28 marine fatalities involving passengers and crew on cruise ships between 2002 and 2011. During that time, the association says, 223 million people (passengers and crew) sailed on cruise ships. And bookings remain robust despite recent accidents, including the capsizing of the Costa Concordia last year, in which 32 people died.
But there are concerns about how the new generation of mega-ships can be evacuated.
The International Maritime Organization, which regulates shipping worldwide, has introduced new regulations for ships longer than 120 meters built since 2010. Known as "safe return to port," the guiding principle is that a ship is its own best lifeboat. So the International Maritime Organization sets out the amount of damage a ship should be able to sustain from fire or flood while remaining seaworthy, and includes requirements for auxiliary power that could support evacuation for at least three hours.
Patchwork of regulation
Even so, regulating the cruise industry is a haphazard business. Many of the International Maritime Organization's pronouncements are in the form of guidelines and recommendations, and rely on national authorities for their enforcement. Cruise ships operating out of ports such as Galveston, Texas, and Miami carry mainly American passengers but are rarely registered in the United States. For example, many of Carnival's liners are registered in Bermuda and the Bahamas.
Another criticism leveled at the cruise lines is that they use foreign flags to avoid U.S. taxes. Sen. Jay Rockefeller, D-West Virginia, who is chairman of the Senate Commerce and Transportation Committee, said last year that cruise ships "are registered in other countries where they can get cheaper labor and they pay no taxes in this country."
Rockefeller said the cruise industry was in a "world of its own."
"They don't reimburse the Coast Guard, they don't pay taxes that will help with the 20 federal agencies that are watching over them in various ways."
From 2004 to 2011, Carnival paid an effective rate of 1.1% in federal, state and local taxes on $11.3 billion in profits. The CLIA acknowledges there "are some fees and taxation considerations " in incorporating overseas, but says cruise lines pay the taxes in the United States they are required to.
Rockefeller wrote of the Triumph in a letter to the Coast Guard. "This horrible situation involving the Carnival Triumph is just the latest example in a long string of serious and troubling incidents involving cruise ships. Safety must be the No. 1 priority in any transportation industry. It is time that the cruise line industry -- which earns more than $25 billion a year -- pays for the costs they impose on the government since it's the Coast Guard that comes to the rescue every single time something goes wrong on a cruise ship."
Critics charge that "foreign flagging" enables cruise lines to evade tougher U.S. regulations, and allows them to recruit crew members with fewer qualifications from overseas. Cruise line companies defend the practice, saying their operations are global.
The fire aboard the Carnival Splendor was investigated by Panamanian officials, with the help of experts from the National Transportation Safety Board and Coast Guard. A Coast Guard report into the incident is still in draft form.
The fire on the Royal Princess was investigated by maritime authorities in Bermuda, where the ship was registered. Those authorities concluded that securing bolts had not been properly replaced over fuel pipework and the damage was worsened by the failure of the water mist system.
Similarly, the inquiry into the fire on the Triumph will be led by the Bahamian authorities.
Diane Laposta contributed to this report.